Field of the Invention
The present invention relates to a display device and a driving method thereof, and more particularly, to a display device including a panel with a built-in touch panel and a driving method thereof.
Discussion of the Related Art
Touch panels are a type of input device that is included in display devices such as liquid crystal display (LCD) devices, plasma display panels (PDPs), organic light emitting display device (OLED), and electrophoretic displays (EPDs), and enables a user to input information by directly touching a screen with a finger, a pen or the like while looking at the screen of the display device.
Particularly, the demand for display devices integrated with in-cell type touch screen, which include a plurality of built-in elements configuring the touch screen for slimming portable terminals such as smart phones and tablet personal computers (PCs), is recently increasing.
In-cell type display devices may be categorized into mutual type display devices and self-capacitive type display devices.
FIG. 1 is an exemplary diagram illustrating a configuration of a related art in-cell display device using a mutual type. FIG. 2 is a waveform diagram showing an image display period and a touch sensing period in the related art in-cell display device using the mutual type. FIGS. 3 and 4 are waveform diagrams of a data line applied to the related art in-cell display device using the mutual type. FIG. 3 (a) and FIG. 4 (a) are exemplary diagrams showing waveforms of a data line. FIG. 3 (b) and FIG. 4 (b) show a touch sync signal for distinguishing an image display period and a touch sensing period.
The in-cell display device using the mutual type (hereinafter simply referred to as an in-cell display device), as illustrated in FIG. 1, includes: a receiving electrode RX that is formed in a block form in parallel with a data line in a display area 11 of a panel 10; a driving electrode TX that is configured with a plurality of driving electrode parts 11 disposed with the receiving electrode RX therebetween in the display area 11 and is formed in parallel with a gate line; a display driver 50 that is provided in a non-display area of the panel 10, controls signals output to the data line and the gate line, and applies a common voltage or a sensing pulse to the driving electrode TX and the receiving electrode RX; a receiving electrode line that extends from the receiving electrode RX, and is connected to the display driver 50; a driving electrode line that extends from the driving electrode part 11 in parallel with the data line, and is connected to the display driver 50; and a touch sensing unit (not shown) that determines whether there is a touch, by using the driving electrode and the receiving electrode which are connected to each other through the display driver 50.
As described above, in the related art in-cell display device, as shown in FIG. 2, a period (hereinafter simply referred to as one frame period) corresponding to one frame is divided into the image display period and the touch sensing period.
That is, the related art in-cell display device simultaneously performs an image display function and a touch sensing function. A plurality of common electrodes for image display performs a function of the driving electrode when the panel 10 operates in a touch sensing mode.
Therefore, a touch panel applied to the in-cell display device includes the driving electrode TX, which is supplied with a common voltage in the image display period and is supplied with a sensing pulse in the touch sensing period, and the receiving electrode RX that is supplied with the common voltage in the image display period and is supplied with a reference voltage in the touch sensing period.
In this case, in the image display period, the common voltage is supplied to the driving electrode TX and the receiving electrode RX. Also, in the touch sensing period, a sensing pulse is supplied to the driving electrode TX, and the reference voltage is supplied to the receiving electrode.
When one frame starts, the image display period is first performed, and after the image display period, the touch sensing period is performed. However, the order where the image display period is performed and the order where the touch sensing period is performed may be switched.
In the related art display device having the above-described configuration, during the touch sensing period, a plurality of the data lines may be connected to ground GND, or may be maintained in a floating state.
First, during the touch sensing period, the data lines may be connected to ground GND so as to stabilize the data lines.
The receiving electrode that is disposed in the same direction as that of the data line is formed in the panel 10 so as to overlap the data line, and thus, when the data line is connected to ground, a capacitor is formed between the data line and the receiving electrode RX. The capacitor formed between the data line and the receiving electrode RX is a parasitic capacitor of the receiving electrode RX.
Due to the parasitic capacitor, as shown in FIG. 3, noise occurs in the data line. The parasitic capacitor of the receiving electrode RX reduces performance in which the touch sensing unit determines whether the touch panel is touched.
Second, when the data lines are connected to ground during the touch sensing period, as described above, the parasitic capacitor is formed, and thus, a touch sensitivity of the touch sensing unit can be reduced. In order to increase the touch sensitivity of the touch sensing unit by decreasing the number of the parasitic capacitors, the data lines may be maintained in a floating state during the touch sensing period.
However, in a state where the data line is floated, when whether the touch panel is touched is determined, whether a first driving electrode TX1 is touched cannot normally be performed due to instability of the data line.
For example, as shown in FIG. 4, in order to decrease the number of the parasitic capacitors, when the data line that holds an arbitrary data voltage during the image display period (which denotes a period labeled “Display” in FIG. 4) is changed to a floating state in the touch sensing period (which denotes a period labeled “Touch” in FIG. 4), the data line is unstably maintained according to an arbitrary voltage value which is held during the image display period.
In this state, when the sensing pulse is supplied to the driving electrode TX for touch sensing, a coupling component is generated between the sensing pulse and a voltage of the data line. A plurality of the coupling components are generated in different sizes in the first driving electrode TX, which is first supplied with the sensing pulse, and the driving electrodes (including a second driving electrode TX2) which are supplied with the sensing pulse after the first driving electrode TX1.
Therefore, a deviation of a plurality of sensing signals respectively received from the driving electrodes subsequent to the first driving electrode can occur.
During the touch sensing period, when the data line is connected to ground, a parasitic capacitor is formed between the data line and the receiving electrode RX, and thus, a touch sensing function is reduced. During the touch sensing period, when the data line is maintained in a floating state, a deviation of a sensing signal (received from a driving electrode which is first supplied with the sensing pulse) and a plurality of sensing signals respectively received from the other driving electrodes occurs, and thus, touch sensitivity is reduced.
To provide an additional description, in FIG. 3 (a) and FIG. 4 (a), an area illustrated as TX1 denotes a timing when the sensing pulse is supplied to the first driving electrode TX1, and an area illustrated as TX2 denotes a timing when the sensing pulse is supplied to the second driving electrode TX2. That is, when the data line is connected to ground or is maintained in a floating state, as shown in FIG. 3 (a) and FIG. 4 (a), an unstable voltage is induced to the data line while the sensing pulse is being supplied to the first and second driving electrodes, and thus, whether the first and second driving electrodes are touched cannot accurately be performed.